Common failure forms and causes of rolls

Roll is to make (rolling material) metal plastic deformation tool, is to determine the efficiency of the mill and rolling quality of the important consumption parts. Roll is an important part of the steel mill rolling mill, the use of a pair or a group of rolls rolling pressure to roll mill steel. It is mainly subjected to rolling dynamic and static load, wear and temperature changes.
We usually use two kinds of rolls, cold rolls and hot rolls.


Cold rolls are made of a variety of materials such as 9Cr, 9Cr2, 9Crv, 8CrMoV and so on. This type of roll has two requirements are
1: the surface of the roll must be quenched
2: The hardness of its surface must be in HS45~105.
Hot rolls are generally manufactured materials such as 60CrMnMo, 55Mn2. The type of rolls used in a wide range of fields, can be used in profiles, bars, rebars, high wire, seamless steel pipe, open billet, and some other processing, it has withstood a strong rolling force , intense wear and tear and thermal fatigue effects, and the hot rolls work at high temperatures and allows the diameter of the unit workload within the diameter of the wear and tear, so do not require the surface hardness, but only required to have a high degree of strength, toughness and heat resistance. Hot rolls only use the whole normalized or quenched, surface hardness requirements HB190 ~ 270 hardness.
Roller common failure forms and causes are as follows:
1, cracks.
Roll cracks occur mainly due to excessive localized pressure on the rolls and rolls caused by rapid cooling and heating. Rolling mill, if the emulsion nozzle blockage, resulting in roll local cooling conditions are not good, it will produce cracks. Winter due to lower temperatures, so it is easier to produce cracks than in summer.
2, falling skin.
Cracks continue to develop on the formation of block or sheet peeling, peeling light can be regrinded to continue to use, peeling serious rolls are scrapped.
3, pitting.
Pitting is mainly due to the strip weld or other debris into the mill, so that the roll surface was scratched out of different shapes of the pit. Generally pitted rolls must be replaced. Strip weld quality is not good, rolling operation to the weld should be lifted and pressed to prevent pitting.


4, sticky roll.
Sticky roll is due to the cold rolling process, broken fragments, wave folding and broken edges appear, and due to high pressure instantaneous high temperature, it is very easy to form a steel strip and roll bonding, resulting in small area of damage to the roll. Through grinding, roll surface cracks can continue to use after elimination, but its service life is significantly reduced, and in the future use of easy to peel off the accident.
5, le roll.
Le roll is mainly caused by too much pressure down the strip to produce heavy skin or slight folding and strip run-off to produce heavy skin. Le roll serious, sticky roll, the strip was rolled crack. Le roll slight, strip and rolls have le marks.
6, broken rollers.
Roll breakage is mainly due to overpressure (i.e., rolling pressure is too large), roll internal defects (non-metallic inclusions, bubbles, etc.) and roll temperature is not uniform to produce a stress field and so on.

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